A new fungus Thraustochytrium kinnei n. sp. was isolated for the first time from tidal currents between the island Helgoland and its nearby dune. It is characterized by a habitus and life cycle different from those of related species previously described. These differences allow for an easy identification and thus make the new species a suitable object for ecological studies on lower marine fungi. The presence of lower fungi from the generaThraustochytrium, Schizochytrium andDermocystidum was recorded at 5 permanent stations in the Weser estuary and the German Bight.T. kinnei was found during the period from July to December and only near Helgoland. Its restricted distribution seems to indicate that the new species is a littoral form which is transported in the form of zoospores in the tidal currents. Further investigations on the physiology ofT. kinnei are presently being carried out.